Optical data communication systems rely heavily on semiconductor lasers as optical sources. Such lasers present a number of reliability problems. In the field of telecommunications, where lasers have become quite popular, many of these problems have been resolved.
As a laser ages, it fatigues and becomes less efficient. More power is then required to drive the communication link. Temperature variations can also affect the laser's ability to drive the channel. A laser which is running hot requires more power for proper operation.
The simplest approach to resolving these problems is to fix the laser drive current at a level which provides acceptable performance over expected laser temperature extremes and expected laser lifetime. The problem with this approach is that higher drive current levels hasten laser fatigue, resulting in premature aging. Elevated drive current also increases temperature levels, which can shorten component lifetimes.
Another solution, widely used in telecommunication networks, employs an analog feedback loop to control the laser drive current. A photodetector, mounted in close proximity to the laser source, monitors the laser light as it is emitted. The photodetector generates an analog signal proportional to the intensity of the laser light. This signal is amplified and fed back to adjust the laser drive current.
Recent advances in optical technology suggest that optical channel interconnects will soon be viable for use in massively parallel processing systems. Such systems require large laser arrays to provide for interprocessor communication. Designers of these systems are inclined to borrow from existing telecommunication technology.